The major goal of this proposal is to reveal molecular mechanisms underlying formation and function of critical transcriptional assemblies essential to embryonic stem (ES) cells and cells with induced pluripotency (induced pluripotent stem (iPS) cells). Using bioinformatics and high throughput experimental methods, we will prepare defined domains of critical transcriptional factors controlling cell pluripotency and analyze them in their functional associations. Thousands of assemblies will be evaluated by biochemical and biophysical methods to identify the critical ones to be targeted by X-ray crystallography. We aim for determination of three-dimensional structures for about 100 stable multi-component transcriptional assemblies. Each of them will represent a partial image of complicated transcriptional machinery controlling the specific transcriptional landscape of pluripotent cells. We expect that thoughtful analyses of these structures will enable us to establish the proper connections between these partial images and reconstruct a general model for function of critical participants of this transcriptional machinery. We will justify this model and the observed regulatory nteractions within identified transcriptional complexes in mutational and functional studies using iPS cells. The experiments are to be done at multiple sites: The Methodist Hospital Research Institute (Houston), Department of Biochemistry and Biophysics at UCSF, the Gladstone Institute of Cardiovascular Disease (UCSF) and X-ray crystallography by the PSI labs. The proposed structural and functional studies will propel our general knowledge ofthe basic mechanisms controlling cell fate, including those underlying self renewal, differentiation and pathogenesis of cancer. The results of this research will also provide more efficient molecular tools allowing precise control over cell programming and reprogramming. The accumulated structural and functional data would be immediately available to biochemical and clinical researchers, and therefore, would have a major impact on stem cell research as well as regenerative medicine.